This invention relates to expandable endoprosthesis devices, generally known as stents, which are designed for implantation in a patient's body lumen, such as arteries or blood vessels to maintain the patency thereof. These devices are particularly useful in the treatment and repair of blood vessels after a stenosis has been compressed by percutaneous transluminal coronary angioplasty (PTCA), or percutaneous transluminal angioplasty (PTA), or removed by atherectomy or other means.
Stents are generally cylindrically-shaped devices which function to hold open and sometimes expand a segment of a blood vessel or other lumen such as a coronary artery.
A variety of devices are known in the art for use as stents and have included balloon expandable stents having a variety of patterns; coiled wires in a variety of patterns that are expanded after being placed intraluminally on a balloon catheter; helically wound coiled springs manufactured from an expandable heat sensitive metal; and self expanding stents inserted in a compressed state and shaped in a zigzag pattern. One of the difficulties encountered using prior stents involved maintaining the radial rigidity needed to hold open a body lumen while at the same time maintaining the longitudinal flexibility of the stent to facilitate its delivery and accommodate the often tortuous path of the body lumen.
Another problem area has been the limiting range of expandability. Certain prior art stents expand only to a limited degree due to the uneven stresses created upon the stents during radial expansion. This necessitates providing stents with a variety of diameters, thus increasing the cost of manufacture. Additionally, having a stent with a wider range of expandability allows the physician to redilate the stent if the original vessel size was miscalculated.
Another problem with the prior art stents has been contraction of the stent along its longitudinal axis upon radial expansion of the stent. This can cause placement problems within the artery during expansion.
Various means have been described to deliver and implant stents. One method frequently described for delivering a stent to a desired intraluminal location includes mounting the expandable stent on an expandable member, such as a balloon, provided on the distal end of an intravascular catheter, advancing the catheter to the desired location within the patient's body lumen, inflating the balloon on the catheter to expand the stent into a permanent expanded condition and then deflating the balloon and removing the catheter.
What has been needed is a stent which has an enhanced degree of flexibility so that it can be readily advanced through tortuous passageways and radially expanded over a wider range of diameters with minimal longitudinal contraction. The expanded stent must also of course have adequate structural strength (hoop strength) to hold open the body lumen in which it is expanded. The present invention satisfies these needs.